Field of the Invention
The present invention relates to a heat transfer fin for a heat exchanger accommodated in a combustion device and the heat exchanger using thereof.
Description of the Related Art
A conventional heat exchanger accommodated in a combustion device, such as a water heater and a heat source device for a room heater, includes a heat exchanger body having an upper opening and a lower opening, a plurality of heat transfer fins, and a plurality of heat-transfer tubes. The plurality of heat transfer fins are disposed in parallel with each other in the longitudinal direction of the heat exchanger body with predetermined clearances between the respective heat transfer fins. The plurality of heat-transfer tubes are disposed so as to penetrate the heat transfer fins in the direction perpendicular to each of the heat transfer fins. According to this type of heat exchanger, the heat transfer fins and the heat-transfer tubes are both made of copper-based metal having high heat conductivity for increasing thermal efficiency. (For example, Japanese Unexamined Patent Publications No. 2001-82808 A and No. 2004-37005 A)
When the conventional heat exchanger recovers latent heat from combustion exhaust gas introduced into the heat exchanger to increase thermal efficiency, steam contained in the combustion exhaust gas condenses on the surfaces of the heat transfer fins into drain. A large amount of drain adhering to and remaining at lower ends of the heat transfer fins may close the clearances between the respective heat transfer fins and obstruct flow of the combustion exhaust gas, which result in lowering thermal efficiency. Further, the combustion exhaust gas contains a large amount of nitrogen oxide. Accordingly, when such acid drain adheres to and remains on the surfaces of the heat transfer fins, the heat transfer fins may corrode.
From the view point of corrosion resistance to the drain, some combustion devices may include heat transfer fins made of stainless steel-based metal. However, heat conductivity of stainless-based metal is inferior to that of copper-based metal. Accordingly, the respective heat transfer fins made of stainless steel-based metal may have partial overheated portions at areas away from the heat-transfer-tube insertion holes, which results in deforming or damaging the heat transfer fins. As a result, thermal efficiency lowers rather than improves. Moreover, residual heat of the heat transfer fins remaining after an operation stop increases as the heat conductivity of the heat transfer fins decreases. Accordingly, due to a so-called post-boiling phenomenon caused by heat transmitted from the heat transfer fins to hot water within the heat-transfer tubes, there is a problem that an initial hot water outlet temperature given to a hot-water supplying terminal may become higher than a set temperature at the time of a restart of operation.